A variety of interface ports or buses exist for enabling communication between a host computer and one or more peripheral devices such as disk drives, printers, and the like. Types of interface buses include the Small Computer Systems Interface (SCSI) bus and a number of parallel buses, including the standard unidirectional parallel port found in early IBM PCS, the bi-directional parallel port, the extended capability port (ECP), the enhanced parallel port (EPP), and the IEEE-1284 standard parallel port. Communication over each of these different interface buses is usually performed in accordance with a communication protocol specific to the particular bus structure.
Unfortunately, the existence of such a variety of interface buses and associated communication protocols creates compatibility problems. For example, a disk drive may be configured to communicate across a SCSI-2 interface while the host computer has a single parallel port interface. Prior to recent advances in the art, such devices that used incompatible bus protocols could not operate together.
In commonly assigned U.S. patent application Ser. No. 08/604,499, filed Feb. 20, 1996, entitled "Multiple Input/Output Port For a Peripheral Device" which is hereby incorporated by reference, there is disclosed a device which provides for connection to multiple bus types. The device comprises an interface bus detection circuit that automatically detects the type of interface bus and a plurality of interface adapters which are employed depending upon the bus type.
Another recent advancement in the art has been in the area of SCSI termination. A SCSI bus must be terminated at both ends for proper operation. If a SCSI bus is not terminated correctly, the devices connected to the bus may not operate correctly or may not function at all. Similarly, terminating at places other than the ends of the bus can result in excessive loading of the cable circuits which could also cause errors.
Prior to recent advances in the art, SCSI termination was done manually. Manual termination proved time consuming and beyond the ability of many users. In commonly assigned U.S. patent application Ser. No. 08/239,999, filed May 9, 1994, entitled "Automatic Termination For Computer Networks" which is hereby incorporated by reference, there is disclosed an apparatus for automatic SCSI termination. In that application, a sense circuit is disclosed that detects whether another device is connected to the device. A switchable terminator responds to the sense circuit to automatically connect the proper terminating impedance.
Thus, a device has been developed for automatically determining the type of port to which a device is connected. Likewise, a device has been developed for automatically terminating a SCSI device. However there are further needs in the art.
It is sometimes necessary to add and remove devices to a computer system while the system is in operation. Often devices are added and removed from a daisy-chain configuration. Furthermore, the host computer port to which a peripheral is attached is sometimes changed during operation of the system. This often results in a change in port type from parallel to SCSI or vice verse. Changing the port type presents the problem whereby when the port type is changed from parallel bus to SCSI bus, it becomes necessary to terminate the last device in the chain. Similarly, changing from SCSI to parallel requires removing termination. Presently, there is no device that recognizes that a change in port type has taken place and activates or deactivates termination as appropriate.
Therefore, there is a need in the art for a device which simultaneously monitors the type of port to which the device is connected, and upon detection that the device is connected to a SCSI port, automatically terminates the device when appropriate.